effect of oil contamination on atterberg limits of soil
TRANSCRIPT
Effect of Oil Contamination on Atterberg Limits of Soil
Ling Tong1, Weisheng Chen1,2, Xilai Zheng2, Mei Li2 1Institute of Environmental and Municipal Engineering, North China University of Water Conservancy
and Electric Power, Zhengzhou, China
2Key Laboratory of Ocean Environment and Ecology, Ministry of Education, Ocean University of China, Qingdao, China
Keywords: crude oil, diesel oil, loamclay, liquid limit, plastic limit
Abstract. Atterberg limit tests were preformed on diesel oil contaminated soil and crude oil
contaminated soil. The results show that Atterberg limits reduced with increasing of diesel oil
content. When crude oil content changed from 0 to 8%, it has little effect on Atterberg limits.
However, it rose from 8% to 16%, plastic limit slightly decreased, but liquid limit increased
remarkably. A "pseudo-viscosity" caused by crude oil is the key factor for this phenomenon.
Introduction
Soil is the main natural resource that the mankind depended on for existence, and it’s one of the
important components of the ecological environment, too. With the rapid development of the
petroleum industry and mass use of petroleum and its products, a large quantity of crude oil and its
products enter into the environment. Worldwide oil pollution and disposal of oil-contaminated soil
have drawn general concern of people. So, further investigation should make on transportation of oil.
And new or better disposal of oil-contaminated soil should be discussed, which may offer scientific
choice for remediation or disposal of oil-contaminated soil and has a value of practical application.
No matter for remediation or disposal, it is necessary to determine properties of contaminated soils
[1].
The objective of this study was to perform laboratory testing programs to determine effects of
crude oil and diesel oil contamination on Atterberg limits of loamclay which are taken from Zibo city
in the North of China.
Materials and Methods
Soil Samples. The soils used in the present experiments were collected from Zibo City, where
petrochemical industry develops rapidly in China. The cropland soil was sampled from the farm land,
40-50cm below the surface of the respective spots. After soil samples collection, the soils were
air-dried, grounded and sized through a screen with 2mm openings, be stored in sealed containers
respectively at room temperature. The properties of the experimental soils are presented in Table 1,
including mineralogy of X-ray Diffraction (XRD) analysis, the grain size distribution and other basic
soil properties. The result showed that the soils in this region are loam clay with a clay percentage of
41.7%, and the loam content of which is 43.5%. Its major mineral is quartz, chlorite and kaolinite.
Chemicals. The crude oil and diesel oil were taken from Qilu Petrochemical Corporation and used
in this experiment as produced without any further treatment. In recent years, various crudes, such as
Shengli, Caoqiao, Gudao and other crude oil, has been used as raw materials of Qilu Petrochemical
Corporation. The used crude oil is light crude, its density was 0.858kg• m-3, freezing point was -12
℃, and viscosity of which was12100mPa• s respectively. The used diesel oil is also light oil, its
density was 0.854kg• m-3, freezing point was -20℃, and viscosity of which was 3.56-4.05mPa• s
respectively.
Sample Preparation. The stored soil was divided into eight parts and then emendated their water
contents. Then the samples were mixed with crude oil in the amount of 0, 1, 2, 4, 6, 8, 12, 16and20 %
by weight. The mixed samples were put into closed containers for 2 month for aging and equilibrium.
Advanced Materials Research Vols. 374-377 (2012) pp 336-338Online available since 2011/Oct/24 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.374-377.336
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Laboratory Testing Method. Liquid limit and plastic limit of soil were determined by
photoelectric detector combined liquid and plastic limits (GYS-2) following Standard for soil test
method (GB/T50123-1999).
Table1 Basic soil properties Minerals
(XRD
results)
quartz albite chlorite and kaolinite calcite illite
43.0 15.2 41.9 - -
Grain size
distrihution
Size(mm) 0.25-0.075 0.075-0.05 0.05-0.01 0.01-0.005 <0.005
Percentage
(%) 3.0 2.0 43.5 9.8 41.7
Basic soil
properties
Texture
Water
Content
(%)
Dry
density
(g/cm3)
Specific
gravity
Void
ratio
Liquid
limit (%)
Plastic
limit (%)
loamclay 13.9 1.54 2.72 0.78 36.4 19.1
Results and Discussion
Influence of Diesel Oil. Atterberg limit tests were preformed on diesel oil contaminated soil
samples and the results were show as Fig.1.It was found that both liquid and plastic limits decreased
with increasing diesel oil contamination. They are basically the same trends, and thus diesel oil has
little effect on the plasticity index (Table 2).
Generally, Clay particles are negatively charged surface. The orientation of polar water around the
clay particles gives clay soils their plastic properties [2-3]. Dry clay soils and clay soil with non-polar
fluids do not have plasticity properties [4]. In this experiment, the test samples were prepared by
mixing diesel oil with air dry soil. Compared with the same water content soil, this dry
diesel-contaminated soil was more like a granular material, soil particles dispersed and show a state
of “sand”. Adding oil decreased adsorption ability of soil and reduces the thickness of double-layer
water. These factors lead to the decrease in Atterberg limits. In addition, adding water to
diesel-contaminated soil samples in the experimental lead to desorption of a part of diesel. The
residual of the part of diesel serve as a fluid medium in soil porosity, thus decreased the amount of
water required for flowing, therefore, lowering the liquid limit.
Plasticity index of clay present the variation range of moisture content in plastic state. The greater
the plasticity index, the more absorption of water, it may also means the more fine particles of soil or
the mineral composition has greater absorption capacity of water. Water molecules are polar but
diesel is a non-polar fluid. While both can be adsorbed by the soil, but the competitiveness of the
water molecule is much larger than the competitiveness of diesel molecules. So, the plasticity index
of diesel-contaminated soil has little difference with the clean soil.
Table 2 Influence of oil content on plasticity index of soil
Oil content (%) 0 1 2 4 6 8 12 16 20
Diesel oil 17.3 18.7 18.4 18.5 19.5 18.1 18.1 20.9 18.0
Crude oil 17.3 15.3 14.8 17.1 16.8 17.6 25.9 27.9 -
Influence of Crude Oil. Fig.2 show that plastic limits decreased with increasing crude oil
contamination, however, liquid limits give some uncertain change. When crude oil content in soil
rose from 0 to 8%, it has little effect on Atterberg limits. However, when crude oil content rose from
8% to 16%, plastic limit slightly decreased, but liquid limit increased remarkably.
The physical properties of the fluid such as viscosity would influence the liquid limit [5]. As
mentioned before, viscosity of diesel was 3.56-4.05mPa•s, but which of crude oil reached up to
12100mPa•s. On the one hand, the thickness of double-layer water of soil particles reduces, on the
other hand, viscosity of crude oil increased plastic of soil. Both them can decreased Atterberg limits.
Advanced Materials Research Vols. 374-377 337
Continue to increase crude oil in soil, coefficient of viscosity gave the contaminated soil some plastic
of itself and its plastic limit decreased. In a sense, the presence of crude oil just likes numerous small
particles of clay. Elimination of the aggregation of soil particles caused by crude oil increase the
amount of water required when the state changed from plastic to liquid. As a result of apparent, liquid
limit increased and the plasticity index increased significantly (Table 2) when the crude oil content
exceed 8%.
0
5
10
15
20
25
30
35
40
45
0 2 4 6 8 10 12 14 16 18 20
oil content (%)
water content (%
)
Plastic limit Liquit limit
0
10
20
30
40
50
0 2 4 6 8 10 12 14 16 18 20
oil content (%)
water content (%
)
Plastic limit Liquit limit
Fig. 1 Influence of diesel on Atterberg limits Fig. 2 Influence of crude oil on Atterberg limits
Discussion. It is known that the plasticity of clay is a phenomenon associated with the clay surface
gravity. The plasticity index is similar positively linear with clay content. So the plasticity index is
usually comprehensive reflection of the mineral composition and particle size of soil. Diesel and
crude oil are two type of oil pollution with different nature, especially in viscosity. It can be seen from
the influence of them on Atterberg limits that the adsorption capacity of soil surface on diesel is far
less than that on water. Diesel just act as a fluid medium. Excess diesel was easily displace by water
and presented as a free-state flow. So the plasticity index of diesel contaminated soil was not affected
by diesel content. While crude oil wrapped contaminated soil particle surface, like millions of tiny
clay attached to the surface. Although mechanical factors of soil not really changed, but a
"pseudo-viscosity" caused by crude oil enhance plasticity and make flowing difficult, result
decreasing in plastic limit, increasing in liquid limit, and the plasticity index increased corresponding.
Conclusions
Atterberg limits results indicate that, Atterberg limits of diesel contaminated loamclay reduce with
increasing of oil content and the plasticity index changes lightly. The “pseudo-viscosity” caused by
crude oil leads to reducing of plastic limit and rising of liquid limit, which makes the plasticity index
increase.
Acknowledgements
The study is financially supported by the National Natural Science Foundation of China (No.
40572142; No.40872150) and the Scientific Research Foundation for high-level talents at North
China University of Water Conservancy and Electric Power (No. 200906).
References
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(2007), p220-229
[3] Das,B.M. Principle of Geotechnical Engineering, 3rd edition. PWS Publishing Company, 1994,
p436
[4] Gillott, J. E. Clay in Engineering Geology. Elsevier.1987
[5] Meegoda,N.J.,Ratnaweera,P.: Geotechnical Testing Journal. Vol.17(1994),p101-112
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